1. Field of the Invention
The present invention relates to a laser diode and an information processor using the same particularly such as an optical disk device or a laser printer using a semiconductor laser device (hereinafter called laser device or laser) which can control the beam divergence and the dot size of a light spot by controlling the size of beam emitting area.
2. Description of the Prior Art
FIG. 2 shows expressions of the print density of a conventional laser printer. In this drawing, the light beam scans from left to right and is irradiated in the hatched parts. In FIG. 2(a), the dot size of the light beam does not change and the print density is expressed by the magnitude of the dot density. In a part with a high print density, the dot density is increased so as to make the print deep, while, in a part with a low print density, the dot density is decreased so as to make the print light. To express a fine half tone using this method, a method that the dot density is increased by using a light spot with a small dot size so as to increase the number of light scanning lines and the light modulation count can be considered. However, since a mechanical method such as a polygon mirror is used to scan the light beam, the scanning speed cannot be easily improved and the number of scanning lines cannot be easily increased. An increase in the light modulation count increases the control time and lowers the print speed.
FIG. 2(b) shows an example wherein the magnitude of the dot density is expressed by changing the light beam shape. In this method, a long and narrow light spot is used in a part with a high dot density perpendicularly to the light scanning direction, and the number of light scanning lines and the light modulation count can be reduced. Japanese Patent Application Laid-Open No. 62-275214 shows an example of a focus variable element for changing the focal position of a light beam that is installed outside the laser, as shown in FIG. 3(a). In this case, fine adjustment for leading the laser beam to the focus variable element is required and it is extremely difficult to establish such a process. In S. Mukai et al, Applied Physics Lett. Vol. 54, No. 4, 23 Jan., 1989, pp 315 and 316, a semiconductor laser device that changes the shape of a light beam emitted from a laser diode by connecting a semiconductor element which serves as an another lens to the laser diode emitting a light beam in a predetermined shape is indicated. FIG. 3(b) shows an example of the configuration of the above semiconductor laser device. This semiconductor element changes a current flowing through the semiconductor element, changes the emission status of the light beam supplied from the laser diode, and changes the focal position of the light spot. This semiconductor laser device requires no adjustment when the semiconductor element is installed and can be made compact, though a technique for connecting the semiconductor element to the laser diode is required.
A light beam spot in a predetermined shape is used for recording, reproducing, or deleting an optical disk device, and an area necessary for recording, reproducing, or deleting information is obtained by the magnitude of the laser output power as shown in FIGS. 4(a) and 4(b). FIG. 4(a) shows an example of change of the laser output power with time during recording, and FIG. 4(b) shows an example of temperature distribution on a disk. The low laser output power P1 shown in FIG. 4(a) is equivalent to deletion and the area W1 where the temperature on the disk us higher than T1 shown in FIG. 4(b) is an area to be deleted. The high laser output power P2 is equivalent to recording and the area W2 where the temperature on the disk is higher than T2 is an area to be recorded. For overwriting with undeleted data minimized (W1&gt;W2), the optical disk materials and laser beam accuracy have been improved.